When reading it, the White House spokesman did not exactly sound as if he believed it himself, to my ears at least. Claims that GCHQ helped Obama bug Trump in the lead-up to the presidential elections have been described as "nonsense" by GCHQ.
If Mr Trump is looking for credibility on the world stage, he should listen to evidence on everything and act on hard evidence. It is always wise to check facts. Take for example global warming. He does himself no favours by acting without reading and accepting the facts. Any leader must work from facts. A politician who does not is living in a bubble.
See http://www.bbc.co.uk/news/uk-39300191. Oh sorry, the BBC is a "false news" supplier!